02/17/05CISC640/440 OpenGL Tutorial1 OpenGL Tutorial CISC 640/440 Computer Graphics TA: Qi Li/Mani Thomas

02/17/05CISC640/440 OpenGL Tutorial2 OpenGL: What is It? GL (Graphics Library): Library of 2-D, 3-D drawing primitives and operations –API for 3-D hardware acceleration GLU (GL Utilities): Miscellaneous functions dealing with camera set-up and higher-level shape descriptions GLUT (GL Utility Toolkit): Window-system independent toolkit with numerous utility functions, mostly dealing with user interface

02/17/05CISC640/440 OpenGL Tutorial3 OpenGL Geometric Primitives GL_QUAD_STRIP GL_POLYGON GL_TRIANGLE_STRIP GL_TRIANGLE_FAN GL_POINTS GL_LINES GL_LINE_LOOPGL_LINE_STRIP GL_TRIANGLES GL_QUADS

4 Specifying Geometric Primitives Primitives are specified using glBegin(primType);... glEnd(); –primType determines how vertices are combined GLfloat red, green, blue; GLfloat x, y; glBegin(primType); for (i = 0; i < nVerts; i++) { glColor3f(red, green, blue); glVertex2f(x, y);... // change coord. values } glEnd();

5 OpenGL Vertex/Color Command Formats glVertex3fv( v ) Number of components 2 - (x,y) 3 - (x,y,z), (r,g,b) 4 - (x,y,z,w), (r,g,b,a) Data Type b - byte ub - unsigned byte s - short us - unsigned short i - int ui - unsigned int f - float d - double Vector omit “v” for scalar form– e.g., glVertex2f(x, y) glColor3f(r, g, b) glColor3fv( v )

02/17/05CISC640/440 OpenGL Tutorial6 OpenGL 3-D coordinates Right-handed system From point of view of camera looking out into scene:  +X right, - X left  +Y up, - Y down  +Z behind camera, - Z in front Positive rotations are counterclockwise around axis of rotation

02/17/05CISC640/440 OpenGL Tutorial7 Transformations in OpenGl Modeling transformation Viewing transformation Projection transformation

02/17/05CISC640/440 OpenGL Tutorial8 Modeling Transformation Refer to the transformation of models (i.e., the scenes, or objects) Generally, –glMultMatrixf(M_i) Some simple transformations –Translation: glTranslate(x,y,z) –Scale: glScale(sx,sy,sz) –Rotation: glRotate(theta, x,y,z) x,y,z are components of vector defining axis of rotation Angle in degrees; direction is counterclockwise

02/17/05CISC640/440 OpenGL Tutorial9 Viewing Transformation Refer to the transformation on the camera Using glTranslate*() and glRotate*() Using gluLookAt() –gluLookAt (eyeX, eyeY, eyeZ, centerX, centerY, centerZ, upX, upY, upZ) eye = (eyeX, eyeY, eyeZ) T : Desired camera position center = (centerX, centerY, centerZ) T : Where camera is looking up = (upX, upY, upZ) T : Camera’s “up” vector

02/17/05CISC640/440 OpenGL Tutorial10 Viewing Transformation from Woo et al

02/17/05CISC640/440 OpenGL Tutorial11 Projection Transformation Refer to the transformation from scene to image Orthographic projection –glOrtho (left, right, bottom, top, near, far) from Hill

02/17/05CISC640/440 OpenGL Tutorial12 Projection Transformation Refer to the transformation from scene to image Orthographic projection –glOrtho (left, right, bottom, top, near, far) Perspective projection –glFrustum (left, right, bottom, top, near, far)

02/17/05CISC640/440 OpenGL Tutorial13 Projection Transformation Refer to the transformation from scene to image Orthographic projection –glOrtho (left, right, bottom, top, near, far) Perspective projection –glFrustum (left, right, bottom, top, near, far)

02/17/05CISC640/440 OpenGL Tutorial14 Notes on openGl transformations Before applying modeling or viewing transformations, need to set glMatrixMode(GL_MODELVIEW) Before applying projection transformations, need to set glMatrixMode(GL_Projection) Replacement by either following commands glLoadIdentity(); glLoadMatrix(M); Multiple transformations (either in modeling or viewing) are applied in reverse order

02/17/05CISC640/440 OpenGL Tutorial15 Notes on openGl transformations Before applying modeling or viewing transformations, need to set glMatrixMode(GL_MODELVIEW) Before applying projection transformations, need to set glMatrixMode(GL_Projection) Replacement by either following commands glLoadIdentity(); glLoadMatrix(M); Multiple transformations (either in modeling or viewing) are applied in reverse order